In the semiconductor industry, there are mainly two types of power MOSFET, namely a Vertical Double-Diffused MOSFET (VDMOS) and a Lateral Double-Diffused MOSFET (LDMOS). Among them, LDMOS transistors may have many advantages over VDMOS transistors. For example, LDMOS transistors may have better thermal and frequency stability, higher gain and ruggedness, lower feedback capacitance and thermal resistance, as well as constant input impedance and a simpler bias current circuitry.
A typical N-type LDMOS structure is shown in FIG. 1. It includes a semiconductor substrate (not shown) and a P-well 100 created in the semiconductor substrate, an N-type drift region 101 formed within the P-well 100; a shallow trench isolation structure 104 formed within the N-type drift region 101 for increasing the channel length of the LDMOS transistor, which may in turn increase the breakdown voltage of the LDMOS transistor; a P-type body region 106 formed within the P-well 100 onside of the N-type drift region 101; a gate structure 105 formed on the semiconductor substrate where the gate structure 105 laterally on the P-type body region 106 and the N-type Drift region 101 and covers a portion of the shallow trench isolation structure 104. The gate structure 105 may include a gate dielectric layer formed on the semiconductor substrate, a gate electrode formed on the gate dielectric layer, and sidewall spacers formed on both sides of the gate dielectric layer and the gate electrode. A drain region 103 is formed in the N-type drift region 101 along with a source region 102 formed in the p-type body region 106, where the source region 102 and the drain region 103 are located on two sides of the gate structure, respectively, and, adjacent to the gate structure 105. Both the source region 102 and the drain region 103 are formed with N-type doping.
However, the performance of the existing LDMOS transistors still needs to be improved. For example, the operating current of the existing LDMOS transistors needs to be increased. The disclosed transistors and fabrication methods are directed to solve one or more problems of the current LDMOS transistors.